Field of the Invention
The present invention relates to an image sensor unit, a paper sheet distinguishing apparatus, an image reading apparatus, and an image forming apparatus.
Description of the Related Art
There is an image sensor unit including a light source, a rod-shaped light guide, and a rod-shaped light condenser (for example, rod-lens array), wherein the light guide converts light emitted by the light source into a line light source (shapes the light into a line) to illuminate an illuminated object, and the light condenser condenses the reflected light. Patent Document 1 discloses such an image sensor unit, wherein the light guide and the light condenser are arranged in parallel, and a partition wall provided on a frame is placed between the light guide and the light condenser. Patent Document 1 further discloses a configuration, wherein notches are formed at a plurality of parts of the partition wall, and the notches are filled with (piled up with) an adhesive for bonding the light condenser to the image sensor unit.
It is preferable that the light emitted to the illuminated object is uniform throughout the whole length. However, leak light may be generated from the light guide, and the amount of light emitted to the illuminated object may be nonuniform when the leak light reaches the illuminated object. For example, when the notches for filling the adhesive are formed on the partition wall, the leak light from the light guide may pass through the notches and reach the illuminated object. Consequently, the amount of light emitted to the illuminated object becomes locally larger at the parts provided with the notches than at other parts. As a result, the uniformity of the output may be reduced. In the image sensor unit, it is preferable that the output is similar (tendency of output is the same) even when the illuminated object is displaced in a light axis direction of the light condenser (even when the position in the light axis direction is different). However, the similarity of output may be broken down according to the configuration described above. Such a problem easily occurs when the size and the width of the frame of the image sensor unit are reduced, and the distance between the light guide and the light condenser is close.